1. Bohr-Rutherford Diagrams for Neutral Atoms
13p
14n

2. The Bohr – Rutherford Model of the Atom
The protons and neutrons are in the nucleus.
Electrons orbit the nucleus in spaces called shells or orbitals.
There are a maximum number of electrons per orbital.

3. Orbitals or Shells
Electrons cannot be found between orbitals, but can move up or down from one orbital to another
Electrons closer to the nucleus have less energy, electrons farther from the nucleus have more energy.

4. Orbital Trends in the Periodic Table
2 orbitals
Period 3 -
3 orbitals
Period 4 -
4 orbitals

5. Drawing Bohr-Rutherford Diagrams
Bohr-Rutherford diagrams represent the arrangement of protons, neutrons, and electrons in an atom of an element.
In these diagrams, the number of protons and neutrons is written in a central circle to represent the nucleus of the atom.
This is the nucleus of lithium. 3p 4n

6. Drawing Orbitals
Circles are drawn around the nucleus to represent orbitals, and electrons are shown in these orbitals.
The number of orbitals for an element is the period number.
The maximum number of electrons in an orbital is the number of the elements in the period.

7. Lithium: Bohr-Rutherford Diagram
Lithium (Li)
Atomic Number=3
Atomic mass = 7 3p 4n
# protons = 3
# electrons = 3
# neutrons = (7-3) = 4

8. Rules for adding electrons to orbitals
The first orbital can hold up to 2 electrons.
The second and third orbitals can hold up to 8 electrons.
When filling orbitals with electrons, place the first 4 electrons at a compass point before pairing.

9. Aluminum: Bohr-Rutherford diagram
Aluminum (Al)
Atomic Number = 13
Atomic mass = 27
13p
14n
# protons = 13
# electrons = 13
# neutrons = 14

10. Valence Electrons
The electrons in the outer orbital are called VALENCE ELECTRONS 3p 4n
How many valence electrons does lithium have?
Just 1!
The number of valence electrons depends on the group number in the periodic table.

11. Valence Electron Trends
Group 1
1 valence e-
Group 13:
3 valence e-
Group 15
5 valence e-
Group 17
7 valence e-
Group 18
8 valence e-
(2 for He)
Group 16
6 valence e-
Group 2:
2 valence e-
Group 14:
4 valence e-

12. Summary First circle = nucleus, write # protons and # electrons
Determine the period and draw one orbital for each period
Determine the number of electrons and draw in the correct positions
Starting in the first orbital draw in a max of 2 electrons always at the top
Move to the second orbital for a max of 8 electrons, one in each compass point, then in partners
Move to the third orbital for a max of 8 more electrons
Complete Bohr – Rutherford diagrams for the first 20 elements